June 22, 2000

A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.

The Wailuku River: mo`o and lava

The Wailuku River is an important landmark to geologists, because it marks
the approximate boundary between the lava flows of Mauna Kea and Mauna Loa.
It is the state's longest river and the southernmost that carries water all
year. An average of 1 million cubic meters (275 million gallons) of water
flows through the Wailuku to Hilo daily, generating some of the electrical
power used on the Big Island. During intense storms, the discharge can be
more than 20 times greater. On average, the Wailuku transports
approximately 10 tons of suspended sediment into Hilo Bay each day.
Hawaiians were impressed by the Wailuku and wove a dramatic tale around
several interesting geologic features within the river. Hina, the mother of
Maui, lived in the cave beneath Rainbow Falls, concealed by the mist of the
falls. Each day she beat and dried her kapa in the sun. A large lizard
named Mo`o Kuna occasionally disrupted this tranquil scene by sending
torrents of water and boulders over the falls.

During a particularly intense storm, Mo`o Kuna moved a huge boulder over
the falls and into the river, where it fit perfectly and prevented water
from flowing farther. Water level beneath the falls began to rise. Hina,
realizing her danger, signaled her son. With two powerful strokes, he
paddled his canoe from Maui to the mouth of the Wailuku. He rushed upstream
and split the damming boulder with a single blow, thereby saving his
mother.

By this time, Mo`o Kuna had fled upstream. Maui found him hiding in a hole
beneath the river. He tried to spear Mo`o Kuna, but the lizard escaped and
rushed downstream. Finally, the mo`o found deep hiding holes and thought he
was safe. Maui again found him and called upon Pele to send lava into the
river to drive out the mo`o. When the lava reached the hiding hole of the
mo`o, the water boiled, sending steam high into the air. The mo`o was
killed; Maui carried its carcass downstream and threw it over Rainbow Falls
for his mother to see.

Maui's canoe can be seen in the river just above the Pu`ueo bridge. It is
part of a lava channel within the river, many other sections of which are
also visible. People knowledgeable about Rainbow Falls can look into its
plunge pool and see the remains of Mo`o Kuna.

The last hiding place of the mo`o is at Boiling Pots in Wailuku River State
Park. Deep potholes eroded into old lava flows and probably connected below
water level can become turbulent during winter storms and appear to be
boiling. At least two lava flows from Mauna Loa filled earlier river
channels. The oldest, the `Anuenue flow, is 10,500 years old. It forms the
thick lip of Rainbow Falls and most of the rounded, gray boulders at
Boiling Pots.

What the Hawaiians probably realized (and what you see today) is that many
of these ` boulders are frozen into a younger pahoehoe flow, named after
the Punahoa ahupua`a and about 3,100 years old. Tracing the flows up and
down the Wailuku tells a geologic story of a river that had already deeply
cut into Mauna Kea and Mauna Loa flows when it was filled by the `Anuenue
flow over 10,000 years ago, probably creating clouds of steam. The filling
caused the river to shift in many places and resume its erosional
downcutting before lava again ventured into the river 3,100 years ago.
These events took place before anyone could have witnessed them, yet the
Hawaiian and the geologic versions of the Wailuku River story have many
similarities. Giant reptiles never lived in Hawai`i, but nonetheless be
respectful of pools of water within the river - a favorite resting place of
the mo`o.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the
past week. Lava is erupting from Pu`u `O`o and flowing through a network
of tubes toward the coast near the eastern boundary of Hawai`i Volcanoes
National Park. The tube system is well-established, and surface flows from
breakouts of the tube system are seen only occasionally in the coastal
flats these days. Lava is entering the ocean mainly at three locations:
Waha`ula, Kamokuna, and at a site 500 meters (550 yards) to the east of
Waha`ula. The public is reminded that the ocean-entry areas are extremely
hazardous, with explosions accompanying sudden collapses of the new land.
The active lava flows are hot and have places with very thin crust. The
steam clouds are highly acidic and laced with glass particles.

One earthquake was reported felt during the past week ending on
June 22, but our seismic network did not record an event at the reported
time.

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Contact:
hvowebmaster@usgs.govUpdated: 27 June 2000